A cracking catalyst composition for enhancing olefins during cracking of heavier hydrocarbons and gasoline, comprising FCC catalyst, in-situ modified clay based additive, optionally ZSM-5 additive. The catalyst can be present in the form of microspheres, pellet, tablet, extrudate and ring and suitable for enhancing olefin product yield by cracking heavy feed material derived from atmospheric and vacuum distillation bottoms; FCC bottoms, coker bottoms and hydrocracker bottoms.
Fluid Catalytic Cracking (FCC) technology developed as early as Second World War is one of the most sophisticated and flexible processes and is most preferred today. Catalyst employed in FCC process possess high conversion, selectivity towards gasoline, low coke make, superior thermal and hydrothermal stability due to the usage of faujasite zeolite based derivatives such as NH4Y, HY, USY, REY and REUSY. This zeolite, on account of its unique pore architecture and cages allow several types of reactions such as cracking, cyclization, alkylation, isomerization among intermediate cracked products as well as with different type of hydrocarbon molecules present in the feed and produces desired useful products as well as adequate amount of coke which is exploited for delivering desired heat for sustaining endothermic cracking reactions. This coke make and catalyst deactivation is accelerated while processing heavier feeds containing metals such as vanadium, nickel, iron and higher aromaticity. However, for maintaining good trade between endothermic catalytic cracking and exothermic coke burning, there needs to be balanced catalyst composition which can boost the economy of FCC process. Besides maintaining adequate coke, there are other issues in FCC process. The Faujasite zeolite, which is the key component of FCC catalyst, is based on collection of sodalite cages connected to each other through their 6-member faces. This arrangement of cages create 12 member pore opening having pore diameter about 13.5 A. Further, the sodalite cages themselves have maximum pore opening of about 6.5 A. Thus with this type of pore size distribution, and high acidity of main zeolite component, FCC catalyst can maximize gasoline, diesel and produce little amount of liquefied petroleum gas (LPG) owing to product selectivity. This limitation can be overcome to a large extent by employing ZSM-5 zeolite based additive. Similarly, for overcoming limitation in cracking of bulky poly aromatic hydrocarbons, naphthenes and paraffin molecules present in heavy feed, a special type of additives based on large pore matrix and phosphate are used nowadays. It may be noted, in spite of employing combination of FCC catalyst with the additives, FCC process still suffers from few limitations in producing high value propylene, isobutylene beyond certain limit, and suppress low cost coke, dry gas and DCO. Thus there is a need to develop new additive catalyst and use this product with a balanced combination of other additives in main FCC catalyst to maximize high value product such as gasoline, propylene and LPG with reduction of coke.
Use of silica sol based binder system in the preparation of zeolite promoted catalysts is cited in U.S. Pat. No. 3,867,308 and alum buffered silica-sol is described in U.S. Pat. No. 3,957,689 and these compositions are for maximizing distillates. Binding of low soda Y zeolite with gel alumina and polysilicate has been described in U.S. Pat. Nos. 4,333,857 and 4,326,993.
U.S. Pat. No. 4,987,110 refers to the preparation of attrition resistant FCC catalysts using low soda silica sol, REUSY and aluminum chlorohydrol. Product selectivity of faujasite zeolite (also referred as Y zeolite) based catalysts is restricted to gasoline range molecules, due to the presence of uniform size large pores in the range 6.5 Å and 13.5 Å. For enhancing C3 to C4 selectivity, for the first time ZSM-5 zeolites having pores in the range 5.4 to 5.5 Å, were employed along with faujasite zeolites, in a conventional silica-alumina based binder system and process for this is described in U.S. Pat. No. 3,758,403.
U.S. Pat. No. 6,258,257 refers to a process for producing polypropylene from C.sub.3 olefins by a two-stage fluid catalytic cracking process having two types of catalysts made from zeolites of large pore and medium pore. U.S. Pat. No. 5,286,369 describes a phosphate based binder composition suitable for binding high silica zeolites. U.S. Pat. No. 5,958,818, refers to a Zeolite/clay/phosphate catalyst characterized by their high levels of zeolite stability.
U.S. Pat. No. 4,956,075 describes a catalyst composition containing Mn, a large pore crystalline molecular sieve, and optionally rare earths for catalytic cracking. This catalyst claimed to offer high gasoline selectivity with low coke yields. U.S. Pat. No. 4,880,787 refers to a catalyst compositions of superior hydrothermal stability, capable of increasing gasoline plus distillate, improved coke selectivity and reduced C4 gas yields, are based on framework dealuminated faujasitic zeolite and matrix treated with aluminum and rare earth. US Pat application 20010044372 A1 refers to a coke selective catalyst comprising a crystalline molecular sieve material having a metal deficient framework wherein the residual framework aluminum sites constitute less than 20% of the total T-sites.
U.S. Pat. No. 4,312,744 refers to a process for low coke make cracking catalyst prepared by mixing a zeolitic crystalline aluminosilicate dispersed in a porous carrier material with a solution of rare earth salt, separating a filter cake from the slurry by a means not involving the washing of the filter cake and calcining the filter cake.
U.S. Pat. No. 8,137,534 B2 refers to catalyst systems for use in these processes that decrease yields of undesirable byproducts including dry gas (hydrogen, methane, ethane, and ethylene) and coke. Representative catalyst compositions comprise a highly siliceous zeolite such as silicalite.
WO 2013005225 A1, refers to a process for cracking of higher boiling petroleum feedstock to obtain lower dry gas without affecting the yield of LPG, light olefins and gasoline products; said process comprising, a FCC catalyst component and an additive component, wherein a novel alkaline earth metal varying from 0.01 wt % to 2 wt % has been used along with conventional catalyst components.
U.S. Pat. No. 6,114,267 refers to a process for preparation of fluidized catalytic cracking (FCC) catalyst, comprising silicon stabilized large crystallite sized synthetic faujasite zeolite, aluminum depleted and normal kaolin clay, alumina and silica. The cracking catalyst is highly active and selective for bottom up gradation, it produces less coke and higher gasoline and total cycle oil (TCO) and possesses improved metal tolerance. This catalyst has limitation in producing LPG, rich in propylene beyond certain limit.
U.S. Pat. No. 5,846,402 refers to a process for selective catalytic cracking of a petroleum-based feedstock to produce a product having a high yield of liquefied petroleum gas (LPG) and light olefins having 3 to 4 carbons, the process comprises of employing a solid acidic catalyst comprising ultra-stable Y-zeolite, Pentasil zeolite active material, bottom selective matrix and rare earth.
U.S. Pat. No. 5,389,232 discloses a riser cracking process where 3 wt. % ZSM-5 additive on the catalyst (ZSM-5 is a shape selective high silica zeolite of average 5.4 Angstrom pore opening) was used to increase the yield of C.sub.3/C.sub.4 olefins by 7 wt. % of feed with minimum loss of gasoline yield up to 5 wt. % of feed from base value. However, in this process the major objective was to improve propylene/iso-butylene selectivity, keeping the gasoline yield at maximum. As a result, the maximum LPG yield in this process is only up to 18 wt. % of feed stock.
U.S. Pat. No. 4,980,053 describes a deep catalytic cracking (DCC) process at very low weight hourly space velocity (WHSV) of 0.2-20 hr.−1 and relatively higher Catalyst/Oil ratio of 2-12 as compared to conventional FCC conditions of 100-300 hr.−1 WHSV and 4-8 catalyst to oil ratio. The LPG yield is reported to be in the range of 30-45 wt. % using paraffinic gas oil as feed stock. However, the major drawback of this process is its relatively very high yield of dry gas (6-12 wt. %) and coke (4-9 wt. %) even with paraffinic gas oil as feed stock. Moreover, the process with a very unstable by-product gasoline cut of sizeable quantity (20-35%) requiring further downstream treatment.
From various prior art catalyst compositions, it can be inferred that no single catalyst component can give desired performance and only combination of catalysts can deliver. In spite, the combined catalyst too have limitations in delivering desired high value olefinic product and suppressing undesired coke, DCO beyond certain limit.